1. Field of Use
This invention relates generally to cranes, particularly mobile cranes, having a multi-section telescopic main boom and an optionally usable boom extension which is pivotally connected to the point end of the main boom and is swingable manually between an in-use position where it is axially aligned with and attached to the main boom and a stored position wherein it is reversed and lies alongside and is secured to the main boom.
In particular, the invention relates to an improved boom extension storage means and mechanisms for releasably securing the boom extension in stored position.
2. Description of the Prior Art
U.S. Pat. Nos. 4,318,488, 4,141,455 and 3,968,884 are each assigned to the assignee of the present application and each discloses a mobile crane having a multi-section telescopic main boom, an optionally usable storable boom extension and boom extension storage means for releasably securing the boom extension in stored position alongside the base section of the main boom. In U.S. Pat. No. 4,141,455, when the boom extension is in its in-use position, the point end of the main boom is rigidly connected to the base or foot end of the boom extension by means of retractable/extendable attachment pins on the boom extension which are releasably engageable with holes provided in clevises on the point end of the fly section of the main boom. When the main boom and boom extension are disposed in horizontal position, as is the case during attachment or detachment of the boom extension, the attachment pins are vertically disposed on opposite lateral sides of the boom extension. If, in these circumstances, the attachment pins on one lateral side of the boom extension are retracted by means of a manually operable rotatable crank and those on the other lateral side remain extended, then the boom extension can be swung or pivoted manually in a horizontal plane about the extended attachment pins between the in-use position and a position wherein it is reversed and lies alongside the main boom. Boom extension storage means are provided in U.S. Pat. No. 4,141,455 to releasably secure the boom extension in a stored position alongside the main boom. These means comprise front and rear storage mechanisms and each mechanism comprises releasably inter-engageable components mounted on a side of the base section of the main boom and on the confronting side of the boom extension when the latter is disposed alongside the main boom. In particular, these components comprise pin-receptacles welded to the side of the base section and storage pins which are welded to the side of the boom extension and extend axially rearwardly when the boom extension lies reversed and alongside the main boom. Thus, in this prior art construction, the storage means are brought into play as follows. Assume that the main boom is a full-power boom and has all telescopic boom sections fully retracted, except for the outermost fly section which is left slightly extended. Also assume that the main boom and the boom extension rigidly secured thereto has been lowered to generally horizontal position. First, the attachment pins on the appropriate side of the point end of the boom are vertically retracted manually by means of the crank. Then the boom extension is manually swung horizontally about the unretracted attachment pins to a position longside the main boom, wherein the storage pins in both the front and rear storage mechanisms are aligned but not yet engaged with their respective pin-receptacles. Finally, the fly section is fully retracted so that the storage pins enter and engage their respective pin-recepticles and so that the boom extension is thereby stored and secured. Setting up the boom extension requires carrying out the above steps in reverse order. As is apparent, in the prior art U.S. Pat. No. 4,141,455, storing and/or setting up the boom extension for use generally requires two people or several trips by one person back to the operator's cab of the crane from whence main boom extension and retraction is controlled. This is time-consuming and costly. The storage mechanism in the other aforementioned patents pose comparable problems and employ storage mechanisms which are relatively complex and costly.